The objective of the research program is to provide information on the functioning and maintenance of the vertebrate photoreceptor. The program emphasizes the mechanism of action of the rod visual pigment, rhodopsin, in the visual process. In providing basic information on the functioning of the vertebrate photoreceptor, the program may also indicate the basis of operation of other receptors such as osmotic receptors (for blood pressure), pH receptors (for oxygen levels), pain receptors, etc., and other sensory receptors such as hearing, taste, etc. In order to obtain the required information, a variety of techniques have been used. Intracellular recording with perfusion, extracellular recording with perfusion, measurements of respiration, microspectrophotometry, regular spectrophotometry, radioactive tracers, and disc electrophoresis are some of the methods used. The samples used include intact or excised eyes from fruitflies, excised vertebrate retinas, or solution extracts of visual pigment. Information has been obtained on the ionization changes of rhodopsin, on the sulfhydryl groups of rhodopsin, on the sequences of thermal intermediates of rhodopsin in solution and excised retinas, and the ionizable groups and importance of pH changes in the vertebrate photoreceptor. Studies on visually deficient Drosophila mutants have revealed differences in visual pigment and other proteins.